1. Field of the Invention
The present invention relates to an organic EL (Electro-Luminescence) display device.
2. Description of the Related Art
An organic EL display device is constituted such that on each pixel region of a substrate, at least one electrode (for example an anode), a light emitting material layer (or a plurality of organic material layers including the light emitting material layer) and another electrode (for example, a cathode) are formed in a laminated manner. A plurality of these pixel regions are arranged two-dimensionally on the substrate so as to form a display region (an effective display region) which displays images. In each of a plurality of pixel regions, one of a pair of electrodes (for example, the above-mentioned anode and cathode) which sandwich the light emitting material layer may be formed as a common electrode which spreads over a plurality of pixel regions.
In each of the above-mentioned pixel regions, due to an electric current which flows from one of the pair of electrodes which sandwich the light emitting material layer to another of the pair of electrodes through the light emitting material layer, the light emitting material layer is made to emit light and hence, an image is displayed on the display region.
In the organic EL display device, the light emitting material layer is formed of organic material and hence, the light emitting material layer is liable to suffer from the degradation due to moisture or the like. Accordingly, in forming the light emitting material layer, a selective etching method based on a photolithography technique cannot be used. In a manufacturing process of the organic EL display device having the light emitting material layer made of low-molecular-system organic material, in place of the selective etching method, for example, using a vapor deposition shadow mask, light emitting material (organic material) which is vaporized by sublimation or the like is selectively adhered to given positions thus forming (sublimating) a light emitting material layer in a given pattern.
In the manufacturing step of the organic EL display device, a selective etching method which uses an etchant after forming the light emitting material layer cannot be utilized and hence, it is necessary to provide a structural body which insulates a pair of laminated electrodes at both sides of the light emitting material layer in the pixel region before forming the light emitting material layer. To cope with such a request, there has been known a technique in which an insulation film (a bank film) in which a recessed portion is formed is preliminarily formed at portions where the light emitting material layer is formed.
In this case, one electrode (hereinafter referred to as pixel electrode) is formed as a layer below the light emitting material layer and another electrode (hereinafter referred to as a counter electrode) is commonly formed on respective pixel regions and hence, the counter electrode is usually formed such that the counter electrode covers the light emitting material layer and the surface of the bank film (see Japanese Unexamined Patent Publication Heill (1999)-329741).
Conventionally, as the bank film, an organic material layer (for example, made of resin) which can be easily formed is generally used. The bank film made of the organic material is formed with a thickness (layer thickness) of approximately 1 μm. On the other hand, a method which forms the bank film using the inorganic material has been proposed (see Japanese Unexamined Patent Publication 2001-68267).